[java-services] Update java, gradle and OTel agent versions

[julianocosta89]

Changes

This PR updates the java version on AdService to latest LTS Java (21).
Unfortunately, there is jvm target 21 for Kotlin yet, so for FraudDetection I've just update gradle to version 8.4.
Also bumped the Java OTel agent in the 3 services its being used.

Merge Requirements

For new features contributions please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[cedricziel]

lgtm

[cyrille-leclerc]

It's a great improvement to use Log4j2 so logs can be captured via auto-instrumentation and send through OTLP.

Did you consider enabling otel.logs.exporter=otlp / OTEL_LOGS_EXPORTER=otlp
the same way it is done on the Java adservice (done through an env variable) and the Python recommendationservice (done through code):

• https://github.com/open-telemetry/opentelemetry-demo/blob/1.5.0/kubernetes/opentelemetry-demo.yaml#L7067
• https://github.com/open-telemetry/opentelemetry-demo/blob/1.5.0/src/recommendationservice/recommendation_server.py#L143C5-L143C17

[julianocosta89]

It's a great improvement to use Log4j2 so logs can be captured via auto-instrumentation and send through OTLP.

Did you consider enabling otel.logs.exporter=otlp / OTEL_LOGS_EXPORTER=otlp the same way it is done on the Java adservice (done through an env variable) and the Python recommendationservice (done through code):

• https://github.com/open-telemetry/opentelemetry-demo/blob/1.5.0/kubernetes/opentelemetry-demo.yaml#L7067
• https://github.com/open-telemetry/opentelemetry-demo/blob/1.5.0/src/recommendationservice/recommendation_server.py#L143C5-L143C17

AFAIK otlp is the default logs exporter, isn't it?

In this PR I'm also adding log4j2 to the Kotlin service, so we also have OTLP traces for FraudDetection.
AdService has it already.

Am I missing something @cyrille-leclerc ?

[cedricziel]

The java-otel README for the autoconfigurer states:

| otel.logs.exporter    | OTEL_LOGS_EXPORTER    | List of exporters to be used for logging, separated by commas. Default is `otlp`. `none` means no autoconfigured exporter. |

https://github.com/open-telemetry/opentelemetry-java/blob/57d83344178f578eb5d2f043b0ffc5c42b6719a5/sdk-extensions/autoconfigure/README.md?plain=1#L79

To my understanding, we should be good with the current change that @julianocosta89 is proposing 👍

[cyrille-leclerc]

You are right, nothing to do in the demo. Logs auto instrumentation got enabled by default in 1.27.0 but the release notes of the auto-instrumentation agent didn't mention it, it just appeared on the release notes of he auto-configure-sdk:

• https://github.com/open-telemetry/opentelemetry-java-instrumentation/releases/tag/v1.27.0
• https://github.com/open-telemetry/opentelemetry-java/releases/tag/v1.27.0

[cyrille-leclerc]

Sorry @julianocosta89 and @cedricziel, OTel Logs are disabled by default on the OTel Java Auto Instrumentation agent. Logs will be enabled by default in 2.0. Shall we enable it on the OTel Demo?

See

https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/97d87f3f3b2bc61aa396d71a98387a1e857618af/javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/OpenTelemetryInstaller.java#L31

And

• Enable OTLP logs exporter by default in the javaagent 2.0 opentelemetry-java-instrumentation#9008

[julianocosta89]

@cyrille-leclerc the logs are already enabled for AdService, and this PR adds it to the FraudDetectionService.

I'm not sure what you would like to add.

Please feel free to send a PR with your suggestions.